As used herein, the term ‘dynamic range’ (DR) may relate to a capability of the human psychovisual system (HVS) to perceive a range of intensity (e.g., luminance, luma) in an image, e.g., from darkest blacks (darks) to brightest whites (highlights). In this sense, DR relates to a ‘scene-referred’ intensity. DR may also relate to the ability of a display device to adequately or approximately render an intensity range of a particular breadth. In this sense, DR relates to a ‘display-referred’ intensity. Unless a particular sense is explicitly specified to have particular significance at any point in the description herein, it should be inferred that the term may be used in either sense, e.g. interchangeably.
As used herein, the term high dynamic range (HDR) relates to a DR breadth that spans the some 14-15 orders of magnitude of the human visual system (HVS). For example, well adapted humans with essentially normal vision (e.g., in one or more of a statistical, biometric or ophthalmological sense) have an intensity range that spans about 15 orders of magnitude. Adapted humans may perceive dim light sources of as few as a mere handful of photons. Yet, these same humans may perceive the near painfully brilliant intensity of the noonday sun in desert, sea or snow (or even glance into the sun, however briefly to prevent damage). This span though is available to ‘adapted’ humans, e.g., those whose HVS has a time period in which to reset and adjust.
In contrast, the DR over which a human may simultaneously perceive an extensive breadth in intensity range may be somewhat truncated, in relation to HDR. As used herein, the terms enhanced dynamic range (EDR) or visual dynamic range (VDR) may individually or interchangeably relate to the DR that is perceivable by short-term adaptation though a HVS. As used herein, EDR may relate to a DR that spans 5 to 6 orders of magnitude. Thus while perhaps somewhat narrower in relation to true scene referred HDR, EDR nonetheless represents a wide DR breadth.
In practice, images comprise one or more color components (e.g., luma Y and chroma Cb and Cr) wherein each color component is represented by a precision of n-bits per pixel (e.g., n=8). Using linear luminance coding, images where n≦8 (e.g., color 24-bit JPEG images) are considered images of standard dynamic range, while images where n>8 may be considered images of enhanced dynamic range. EDR and HDR images may also be stored and distributed using low bit-depth, non-linear luminance coding (e.g., 10-bits and logarithmic luminance coding), or high-precision (e.g., 16-bit) floating-point formats, such as the OpenEXR file format developed by Industrial Light and Magic.
Most consumer desktop displays support luminance of 200 to 300 cd/m2 or nits. Most consumer HDTVs range from 300 to 1000 cd/m2. Such conventional displays thus typify a low dynamic range (LDR), also referred to as a standard dynamic range (SDR), in relation to HDR or EDR. As the availability of EDR content grows due to advances in both capture equipment (e.g., cameras) and EDR displays (e.g., the PRM-4200 professional reference monitor from Dolby Laboratories), EDR content may be color graded and displayed on EDR displays that support higher dynamic ranges (e.g., from 1,000 nits to 5,000 nits or more). In general, the methods of the present disclosure relate to any dynamic range higher than SDR.
As used herein, the term “display management” denotes the processing (e.g., tone and gamut mapping) required to map an input video signal of a first dynamic range (e.g., 1000 nits) to a display of a second dynamic range (e.g., 500 nits). Examples of display management processes are described in PCT Application Ser. No. PCT/US2014/016304 (the '304 Application), filed on Feb. 13, 2014, “Display management for high dynamic range video,” by R. Atkins el at., (published as WO/2014/130343) which is incorporated herein by reference in its entirety. Display management may be assisted or controlled by input metadata generated by the source of the incoming content and multiplexed into the coded bitstream.
In some use cases, incoming EDR video may also be blended by graphics of a third dynamic range (e.g., 100 nits) before being sent to the target display. As used herein, the term ‘graphics’ denotes any kind of imagery (e.g., menus, still pictures, vector graphics, video, and the like) that may be blended with a video signal. As appreciated by the inventors here, improved techniques for blending graphics with high dynamic range video are desirable.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.